Why do the popupmenus/ listbox disappear if i use pushbutton callback ?

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VBBV 2018-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/411497-why-do-the-popupmenus-listbox-disappear-if-i-use-pushbutton-callback

评论： Image Analyst 2018-7-22

I have GUI, which has few pushbuttons that loads some data into popupmenus and listbox When I click on pushbutton, to reset the content to empty, it makes the popupmenu /listbox disappear. why does it happen? how can I avoid it ?

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Walter Roberson 2018-7-22

Please do not close questions that have an answer.

Your question is not unclear: you are just asking to do something that cannot be done in MATLAB.

Image Analyst 2018-7-22

If you're got your answer, and are all done, then you can "Accept" the answer (to give the answerer reputation points and let everyone know it's solved) rather than Close the question.

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Answer 1

Walter Roberson 2018-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/411497-why-do-the-popupmenus-listbox-disappear-if-i-use-pushbutton-callback#answer_329790

When you set the String property of the popup or listbox to empty, you need to set the Value property to [] at the same time, or else the Value will be greater than the number of strings and it will consider that an error and refuse to draw the box.

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VBBV 2018-7-22

编辑：VBBV 2018-7-22

when I do that I get a warning message Warning: 'popupmenu' control requires a scalar Value. Control will not be rendered until all of its parameter values are valid Still the popupmenus disappear.